This invention relates to a device generally defined as an automatic focusing device for cameras which electrically detects the proper focus position for the lens and automatically brings the lens into focus position.
The conventional automatic focusing device utilizes the principle of the coincidence type rangefinder in which a pair of photoelectric elements are provided and the lens is fixed at a focus position in response to a focus signal which is produced at coincidence of an image made by a stationary mirror and an image made by a movable mirror coupled with the lens. In this system, when focus detection is impossible, the camera shutter is released with the lens adjusted to a position corresponding to an infinite range or minimum range as the lens driving member is used also for releasing the shutter. Furthermore, this system has the disadvantage that the range indication is recognizable only after the photographing procedure has been completed.
There has been introduced another system in which the operations of the movable mirror and the lens stopping member are coupled with the shutter release operation. In this system, range indication is recognizable before the shutter release operation as the position of the lens stopping member is determined prior to lens driving operation, however, this system has the disadvantage, particularly in a system employing an electromagnetic device for retaining the lens stopping member, that lens stopping member retaining position varies according to the shutter releasing speed as the operating speed of the movable mirror and the lens stopping member varies according to the variation of the shutter releasing speed.
Both of the conventional systems as referred to hereinbefore have the disadvantage that the focusing accuracy is greatly affected by difference between stationary and the movable optical passages or any variation in the sensitivity between the photoelectric elements since the optical system of the coincidence type rangefinder has two optical passages comprising a stationary optical passage and a movable optical passage capable of changing the light intensity distribution informations, and two separate light receiving units each consisting of a plurality of photoelectric elements for receiving incident light through the respective optical passages, for accomplishing the focus detection.
Accordingly, an object of the present invention is to provide an automatic focusing camera of good accessibility and high accuracy.
According to the present invention, in an automatic focusing camera capable of determining the focus position of the lens by automatically detecting the distance between an object to be photographed and the camera, a charged actuating member is released by a shutter releasing member before the shutter releasing member releases the shutter, then the actuating member performs a series of operations from range measurement to retention of the range setting member. In case focus detection is impossible, the actuating member can be restored to the initial position by restoring the shutter releasing member allowing repetition of the series of operations as described above.
Furthermore, the motion of the lens stopping member is not affected by the shutter releasing speed so that the lens stopping member is accurately adjusted to a correct position as the lens stopping member is driven by the actuating member at a controlled speed.
Still further, the present invention improves the accuracy of the range measurement system because range measurement is not affected by a difference in sensitivity between the photoelectric elements or difference between two optical passages since a single image lens and a single unit of photoelectric elements are employed for obtaining light informations through a stationary optical passage and a movable optical passage.